Study On Novel Passive Compound Resonant Cavity Filtered Narrow Linewidth Wavelength-Swept Fiber Laser

With the gradual development and maturity of laser technology,fiber lasers are widely used in optical communications,high-precision measurement,atomic clocks,basic physical quantity measurement and other fields.Wavelength-swept fiber lasers are especially useful in fiber sensing,biomedicine,and spectroscopy.At present,the research and development directions of wavelength-swept fiber lasers are mainly focused on the continuous improvement of scanning speed,scanning range,output power and instantaneous line width.In this paper,work on the application of the new passive composite resonator filter and its wavelength-swept fiber laser is carried out.The main innovations and research contents are as follows:1.For a variety of passive compound-cavity filter,a matrix solution method based on optical path transmission analysis is proposed,which simplifies the filter structure analysis process in the form of nodes and transmission optical paths.The matrix solution method can be used without deriving analytical solutions.Direct numerical solution to obtain the filter spectrum of the composite resonator filter greatly reduces the difficulty of its analysis and simulation.Examples and analysis of several complex passive compound-cavity filters,and simulation analysis methods and filtering spectra are given.It is found that the filtering effect of the dual-coupler ring based compound-cavity(DCR-CC)filter has obvious advantages,and the filter characteristics of the DCR-CC filter are analyzed in detail,and the filter spectrum evaluation standard and parameter selection method are given.Finally,the experimental filter parameters are determined.2.Developed a single longitudinal mode narrow linewidth wavelength-swept fiber laser based on DCR-CC filter and C+L band Erbium-doped fiber amplifier(EDFA).The use of DCRCC filter combined with tunable fiber F-P filter(Fiber Fabry-Pérot tunable filter,FFP-TF)realizes the wavelength-swept laser output with transient SLM oscillation in the C+L band over80 nm.And it can run stably at a scanning frequency of 150 Hz.Use Fiber Bragg grating(FBG)with the same bandwidth instead of FFP-TF to measure the static laser performance of the laser.The laser wavelengths at 1530 nm,1550 nm,1570 nm and 1590 nm all have >66 d B of optical information.Noise ratio,<-153.33 d B/Hz relative intensity noise,<625 Hz laser linewidth,<0.704 d B power fluctuation and no mode hopping occurs within 20 minutes.By calculating the duration of the laser longitudinal mode,it can be known that the instantaneous output laser can reach the linewidth and beam quality of the static output laser under the scanning operation state.3.Taking the erbium-doped fiber laser as an example,starting from the operating principle of Fourier domain mode locking(FDML),the mechanism of the instantaneous linewidth broadening of the FDML wavelength-swept laser is systematically analyzed.At the same time,the dual The filter characteristics of the dual-coupler ring(DCR)in the fast wavelength-swept state,it is proposed that the band rejection filter channel using the DCR filter can filter the laser without destroying the dynamic balance of the FDML.Demonstrated for the first time a highquality Fourier domain mode-locked wavelength scan with an erbium-doped fiber as the laser gain medium,a wavelength scan range of 3.072 nm,an optical signal-to-noise ratio of 57.31 d B,a scan rate of 62.918 k Hz,and an instantaneous linewidth of 4.28 GHz Fiber laser output.After adding the DCR filter,it can be clearly seen from the spectrum that the intensity of the different wavelength components caused by the filter has changed.On the beat spectrum,a series of beat frequency peaks with an interval of 340.60 MHz are observed,and the interval corresponds to the cavity length of 60.00 cm of the DCR.